Electric circuit interrupter



Patented Aug. 5, 1952 ELECTRIC CIRCUIT INTERRUPTER Percy Bartlett, Swarthmore, Pa., assignor to General Electric Company,.a corporation of New York 12 Claims.

This invention relates to electric circuit interrupters for medium and high voltage circuits, and particularly to high speed circuit breakers of the liquid or oil-blast type which are required to interrupt alternating current power circuits within a few half cycles.

More specifically, my invention is directed toward the provision of an improved arc-extinguishing device wherein auxiliary means, such as an impulse piston, are employed for insuring that an arc extinguishing blast is always available, even when interrupting light current arcs such as are encountered when the circuit breaker merely is performing switching operations.

In such a fluid blast interrupter, it is common to produce the necessary blast action for heavy currents through the agency of a pressure-generating series arc. Thus, it is well recognized in the art that the effective interrupting range of a fluid blast circuit interrupter depends, at the lower extreme, upon its ability to interrupt light current arcs and, at its other extreme, upon the ability of the extinguishing structure to withstand without damage the high pressures generated when interrupting heavy current arcs. It also is well understood that arc-interrupting structures may be adapted for the safer interruption of heavy current arcs by the employment of suitable devices for relieving or venting excessive internal pressures as well as utilizing other means whereby the arc lengths, and particularly the length of the pressure generating arc, is controlled in such a way as to generate maximum available pressure for light current interruptions and minimum or moderated available pressure for heavy current interruptions.

In accordance with my invention, I so arrange the impulse piston of an extinguishing device that it augments the arc pressure when interrupting light currents while, on the other hand, it is adapted for relieving or moderating the excessive pressures produced when interrupting current toward the higher limit of the interrupters range.

To this end, I bias the impulse piston of my invention, in the breaker-closed position, to an intermediate position within its enclosing cylinder so that, coincident with the opening of the circuit interrupter, the piston will move in one direction or the other from its pre-set position depending upon whether low arc pressures or high are pressures respectively are generated within the extinguishing structure. My invention further contemplates controlling the length of the pressure generating are by simple means Application July 27, 1949, Serial No. 167,107

\nected in series when the lift rod'5 is in the. upper 2 which prevent heavy current arcs from bowing to undesirable length while permitting, or inviting, light current arcs to bow for the purpose of generating a more efiective blast action at the interrupting arc.

It is, therefore, an object of my invention .to provide a fluid blast circuit interrupter having an impulse piston which is capable of substantial reverse movement for the purpose of moderating excessive pressures generated by heavy current arcs within an arc-extinguishing structure.

It is a further object of my invention to provide a circuit interrupter, the impulse piston of which is capable of substantial reverse movement for increasing the effective volume of theinterrupting structure andthereby moderating excessive pressures generated in the pressure-generating chamber of a liquid blast interrupter.

It is another object or my invention to provide a circuit interrupter the effective volume thereof being caused to decrease or increase respectively in accordance with the magnitude of the current being interrupted or with the arc pressures generated therefrom.

A further object is to provide simple means through the axis of a. conventional tank-type oil circuit breaker employing the interrupter of .my invention; while Fig. 2 is an enlarged perspective view of the pressure-generating arc control member shown in Fig. 1. I

The drawing illustrates a single interrupter element I of a single-pole tank-type oil circuit breaker, .the latter of which ,comprises'aipair of such interrupterswhich depend fixedly from the top cover 2 of an enclosing tank 3 by means of a pair of symmetrically inclined conductor bushings, one of which is indicated by A;

The pair .of interrupters l are disposed well below the level of the dielectric fluid which pref-' erably is oil, the level of which is indicated toward the top of tank 3, and are, electrically con or closed position as shown, in which position the conducting switch blade 6 interconnects the current conducting structures within the interrupters 1 thereby completing a closed circuit through the breaker unit from the external line terminal 1 of the bushing l to the corresponding external terminal of the opposite bushing. Thus, it will be seen that current flowing through the conducting path of the circuit breaker from terminal I to its corresponding opposite terminal constitutes a loop, the magnetic effect of which induces a force tending to displace outwardly the arcs drawn between the separable contacts within the interrupter; i. e. arcs drawn within the interrupter I shown in the drawing will be driven toward the left-hand interior walls thereof. Attention will be drawn later to this tendency of the arcs to bow outwardly within the interrupters.

In a triple-pole circuit breaker, as is Well understood in the art, three of the above-mentioned single-pole units would be arranged in spaced relationship, while a common interconnecting operating mechanism would be provided for lowering or raising the lift rods in unison for effecting a circuit opening or closing operation respectively in the three phases. As is well understood in the art, an appropriate stroke-multiplying straight-line mechanism for the lift rods 5 is disposed in the mechanism housing 8 surmounting the top cover 2.

When the breaker is tripped to open, the lift rod 5 and its switch blade 6 are moved downwardly at high speed, thereby to eifect circuit interruption by extinguishing the arcs drawn in the interrupting structures I as the rod-type contacts 9 carried by the blade 6 are withdrawn therefrom. In well known manner, the downwardly spring-biased intermediate contact It] moves in follow-up engagement with the contact 9 thereby separating from the fixed contact H to draw the pressure-generating are which, for high current interruptions, will furnish adequate pressure for producing the flow of fluid whereby the interrupting are drawn between the intermediate contact I!) and the rod-contact 9 will be cross-blasted through the lateral ports I 2 proceeding outwardly from the lower region of the arc-extinguishing structure I. It Will be observed that the separation distance between the fixed contact II and the intermediate contact I!) is limited by the provision of an appropriate stop means, being in this instance the button 13 which, screwed into the upper end of the intermediate contact I0, constitutes a stop shoulder for. engaging the upper surface of the lamination 14. The latter constitutes an intermediate insulating lamination of the several from which the lower portion of the arc-extinguishing structure is fabricated.

As is well understood in the art, such a stack of insulating plates, having suitable aperturing therein, and strongly bolted together, defines appropriate internal pockets, passages, and vents for the interrupter unit. In the present instance, circular openings in the upper laminations together 'with an aligned cavity provided in the interrupter adapter casting I5 define the annular pressure-generating chamber is about the pressure-generating break. The pressure chamber may be provided with gas vents such as I! to facilitate the re-entry of fluid after each interruption; while a valve disk 18 may be employed, for closing these openings automatically so that pressure is not wastefully dissipated therethrough from the pressure chamber [6 during a circuit interruption. Ample volume for this chamber provides for a rapid reclosing cycle for the circuit breaker.

Appropriate aligned openings in the intermediate laminations of the interrupter structure define one or more vertical blast passages such as 19, and it is well understood that the arc-generated pressure from the chamber I6 is effective to drive a blast of arc-extinguishing fluid down the passageway 19 and transversely through the interrupt-ing arc in the direction of the arrows shown on the drawing to produce an arc-extinguishing cross-blast which effectively sweeps the ionized products of arcing from the interrupter through the lateral vents l2 into the surrounding fluid in the tank 3.

In accordance with one feature of my invention, I provide a substantially cylindrical insulating guard member 20 for closely encircling the pressure-generating break between the fixed contact II and the intermediate contact IE]. This uard member is securely affixed or clamped in this position by any convenient means such, for example, as providing corresponding annular recesses for the reception ofits upper and lower ends in the adapter casting l5 and the lamination 14 respectively as shown in Fig. 1. The guard member 2!! possesses a relatively large opening 2! which, as best seen in Fig. 2, may conveniently be attained merely by removing a short arcuate portion of the members sidewall. Inthe wall of the member 20 remote from the opening 2|, I provide a series of narrow vertical notches 22. The notches directly opposite 2|, such as 22, I make the narrowest, say, on the order of M but I may elect to increase the width of these notches as they are disposed more to either side. For example, I may grade them so that the outer notches 23 might be on the order of or Alternatively, I may choose to employ the minimum of one narrow slot such as 22 opposite to the main opening 2|.

When assembled in the interrupter, and with the interrupter assembled in the tank, the large ports 2| are directed inwardly, that is toward the lift rod 5. With this arrangement, it will readily be perceived that the pressure generated at the pressure-generating break experiences little impediment to its blast action toward the blast passage 19, especially in the case of the interruption of high currents. As explained earlier, arcs drawn within the interrupter have an inherent tendency to bow outwardly so that, if it were not for the presence of my guard member 20, a heavy current pressure-generating arc could elongate to a looped configuration somewhat as indicated by the dotted line 21a. A high current arc of such length drawn in oil can possibly generate pressures excessive enough to damage or destroy the interrupter structure within which the arc is formed. However, the narrow slot or slots 22 of the guard member 20 are not wide enough to permit the passage of an are above a certain intensity so that none but the lighter current arcs, i. e. those having but small diameter, can pass through and elongate to the extended configuration 2m. Such elongation, of course, is desirable and needed in the case of light currents, for a short are in such circumstances too often is unproductive of adequate blast action.

In making the slots 22 vertical, i. e. parallel to the arc path, it will be appreciated that the passage therethrough of small diameter arcs thereby is facilitated. By increasing the width of the slotstoward the sides of the member 20 as indicatedatit, larger arcsmaypass .there-I through than can be accommodated by, slots.22 butthe tendency for such arcs topassthrough slots 23 will be less pronounced becausethe mag.-.

netic blowout action in these divergentdirections is correspondingly less in magnitude. Preferably, the guard member 28 should be made of insulating material which is practically impervious to, and substantially inert under theinfiuence of, an are. It may, for example, be made from some suitable refractory material or from some appropriate asbestos compound. A good material in the latter category'for this purpose is the-socalled phospho-asbestos which is disclosed and claimed in the U. S. Patent 2,356,485 to Brink et al. which is assigned to the same assignee as the present application.

Thus, it will be appreciated that the simple grid-like C-sectional guard member 20 shown in Fig. 2 provides a very economical, and readily renewable, means capable of discriminating among arcs of varying magnitudes for controlling the blast pressure, particularly in an oilblast type of interrupter. Also, it will be understood that I might employ auxiliary magnetic blow-out means, such as coils or magnetic plates and such, for amplifying the arc bowing effect for circuit breakers in which the magnetic bowing forces are inherently weak, as, for example, in power circuit breakers in which the interrupters are widely spaced from one another.

For supplementing the low blast pressures which characterize lower current interruptions as encountered in normal switching duty, it is known to employ auxiliary pressure producing means such as the impulse piston 24' of the drawing. This piston, pressed downwardly by the nest of springs 25 (which has been cocked to the position shown by the blade 6 through the plunger 26), is efiective to supply an auxiliary blast flow indicated by the arrow 21 immediately after the contacts separate whenever the springproduced pressure of fluid in the cylinder 28 exceeds that produced in the passage 19 by the pressure-generating are drawn between the contacts II and H3. Such pistons are usually-provided with a check valve 29 which uncover piston ports to facilitate the piston charging operation during closure of the circuit breaker.

,In accordance with another feature of my invention, I arrange the piston 24 in a cylinder of greater length proportions than is conven tional and, by choosing a charged position at an appropriate normal intermediate position of the piston, I make ample provision for the piston 24 to back up an appreciable distance, indicated by the letter D, in the event that dangerously excessive pressures are generated due to the drawing of a particularly high-current pressuregenerating arc. Accordingly, having pre-selected an optimum blast pressure (say some 209 lbs. per sq. in., which will be effective for extinguishing all'arcs likely to be produced throughout the whole interrupting range of a given circuit breaker) my piston arrangement, spring loaded to produce this fluid pressure, will respond downwardly to augment arc-produced pressures of less retainer 37!...for achieving desiredpiston settings and,springpressuresbest suited for specific or individual applications.

It is believed to be clear from the drawing that the cylinder 28 for the, piston 24 may be defined by aligned openings in the lower insulating laminationsand the upper adapter casting, 1,5 of, the interrupter I. Because the primary moderating purpose of theimpulse piston 24 is to relieve excessive pressures initiated in the chamber [6, I prefer ,to provide the supplementary port 32 leading directlyfrom this region tothe underside of the reversely-moving piston so asto expedite the pistons upward moderating move: ment and effect.v

Thus, it willbe appreciated that the piston24 constitutes virtually a movable and resilient wall whereby the volume of the interrupter I accommodatesitself in accordance with the arc prose sures generated therein; this volume tending at all times to adapt itself to maintaining the desired optimum pressures determined with the setting of the springs 25. To this end, the nest of springs 25 is designed for low gradient so that neither expansion nor further compression thereof will unduly change the loading in either direction.

As a further pressure moderating feature, I may choose to provide pressure-relief vents. which are uncovered by the piston 24 toward the upper range of its travel. These vents, lying in the way of the port 32, provide a generally direct escape to the tank from the annular pressuregenerating chamber [6 on the interrupter I,. Also, instead of placing the pressure reliefvents (it substantially abovethe lower face of the pise ton as shown in the drawing, I may elect to position the vent or vents at the same level, or below, the pistons lower face as indicated by dotted lines at 3311. W In this location, the relief vents perform a double function. In the first place, they facilitate the pistons picking up speed initially after breaker tripping so that, by the time the piston has closed the vent 33a, it will be moving with some momentum for applying its auxiliary blast effect in the event that a light duty. current interruption is being initiated. In the second place, in the event that a high current interruption is being initiated, the piston 24 will barely have shut oif the vent 33a before overpressure generated in the chamber I6 will have caused an instant reversal of the piston so that early pressure-relieving action through 33a is thereby afforded. Moreover, it will be obvious that the port 32 between the pressure chamber I5 and the cylinder 28 may be lowered in a similar manner to correspond to the level of 33a. Furthermore, I may provide a series of more than two vents such as 33a and 33. Such a series may be arranged one above the other, ladder fashion, to provide progressive pressure relief so that, by the time the piston has reached its full upward travel, the piston conceivably may have'opened up a venting area in excess of its'own area. Thus. the interior of the interrupter could be rendered wide open so as to preclude all danger from destruction by blowing apart. Accordingly; by the relatively simple structure employed in the interrupter of my invention, very effective optimum arc-extinguishing blast action is assured for currents over a very wide range from the lowest to the highest; by providing unitary auxiliary pressure-producing means for the former which also constitute pressure ameliorating means for the latter.

In viewoi the above detailed explanation, it is believed that but a brief review or the. operation of the circuit breaker shown here is necessary. In the closed position shown, a mechanism has elevated the lift rod with its blade 6 and the pair of rod contacts Q from their lower open position toward the bottom of the tank 3." In thisupward.

closing movement, the screw head 38 has picked up thepiston plunger 26 and moved the piston 24 against the bias of its springs 25 to the chosen intermediate position in the cylinder 25. Meanwhile, the rod contact 9 has engaged the'intermediate contact iaso that the latter has closed. the gap between its cap l3 and thefixed contactll thereby to complete the breakercircuit from terminal'i' to the opposite terminal. Tripping ofthe breaker; responsive to some protectivev device or from an operator directing a switch-open operation, will cause a high-speed downward movement of the-blade 5 and its associated parts through the agency-of the breakeropening spring (not shown) Theintermediate contact' lfl, urged by its individual biasing spring, moves'in following engagementwith the rod contact 9 to for: an arc gap at the fixed contact l l. The pressureproducing are at this gap instantlygenerates. a pressure, the intensity of which generallyis in accordance with the magnitude of the current being interrupted. In the case of light currents, this arcmay extend itself outwards as shown at 2la,,or, on the other hand, if above a certain current magnitude, the arc will be entrapped within the grid-likeguard member 26 .so that its length is thereby limited. Pressure generated within the guard, however, may pass through the slots 22 and 23.to the pressure chamber it although it will pass more directly toward. the passage 19 through the larger opening 2|. Blast action then. ensues with the extinguishingfluid being forced downward through the'blast passage l9 and out transversely across the interrupting are which has been drawn between the receding contact 9 and the intermediate contact [0; this cross blast dividing and exhausting laterally through theplural vents i2 to the exteriorof the interrupter I. 7

If it has been a light current interruption, the piston 24 will have moveddownwardin followingrelationship to. the blade 6 to provide auxiliary blast'actionfollowing the dotted arrow 21'; but, if the pressure within the interrupter has-exceeded the optimum chosen, by the setting of the springs 25, thepistonzd will have moved upward to moderate this pressure and, if excessi-ve, this pressure-may have been safely expended through the relief vents 33 or 33a. C'oincident with the build up of pressure in the chamber 16, thevalve 18 will have automatically closed the gas vents l1 and conversely, with'the opening of the breaker and extinguishmentoi the are this internal pressure will abate and the valve [8 will reopen. The opened vents I! thereupon provide ready egress for the entrapped gas products'of interruption so that the interrupter iswrapidly replenished with extinguishing fluid from the tank 3'through the blast ports I2 in preparation for a subsequentclosing, or a rapid reclosing, operation.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without. departing from the spirit of my invention. For example, t e .arccontrolling grid-like memberlddescribed herein is not necessarily restricted for use in liquid blast circuit breakers; forit'could be equally effective;

in the case of so-called autoblast breakerswherein blast pressure isgenerated by reason of the arc liberating gas from. vaporizable insulating. solid substances-provided inzor near therarcing zone. Again thepressure-relieving impulse piston dis.-

closed .herein obviously is adaptablenot only tov series. break fluid blast interrupters but it could be applied for augmenting the blast action of single break interrupters such as, for example, the type describedin the U. S. Patent 2,036,800

topEhrenberg et al. which is assignedtothe same assigneej as, thispresent application. Further-- more, thispiston arrangement may be appliedv with beneficial effect to all types of fluid blast interruptersincluding gas-blast and auto-blast power, circuit breakers.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit interrupter-comprising a pressure confining. structure, relatively movable contacts adapted to separate in said structure, an arc.

extinguishing fluid in said structure, means for. separating said contacts to draw an arc-to be extinguished by blast action within said struc-; ture, a cylinder in communication with said structure, a, springpressed piston norma1lydis+ posed inan intermediate position in said cylinder, and means operative duringcircuit closing movement of said interrupter for driving said piston to said intermediate positionwithin said cylinder so that during a circuit opening operationsaid piston moves in one direction for-apply--- ing an impulse blast to the arc immediately after separation of said contacts when the-arc current is below a predetermined value and a substantial distance in the opposite direction for moderating internal fluid pressures when the arc current is above a predetermined value.

2. A- circuit interrupter comprising a pressure confining structure, relatively movable contacts adapted to separate in said structure, an arc extinguishing fluid in said structure, means for separating said contacts to draw an arc to be extinguished by blast action within said structure to produce a circuit-interrupting operation, a cylinder in communication with said structure, a spring-pressed piston normally disposed in an intermediate position in said cylinder, and means operative during circuit closing movement of said interrupter for driving said piston to said intermediate position within said cylinder so that during a circuit opening operation the said piston may move in one direction for applying an impulse blastfor lower current interruptions immediately after separation of said contacts but may move in the opposite direction for moderating internal fluid pressures for higher current interruptions, and venting means from the interior of said structure arranged to be opened in accordance with reverse movement of said piston.

3. A circuit interrupter comprising a pressure confining structure with an arc-extinguishing fluid contained therein, relatively movable contacts adapted to separate in said structure to pro? duce a pressure-generating arc and an interrupting arc, said structure defining a pressure .zone about said pressure-generating arc and an interrupting zone adjacent the interrupting arc, a. communicating blast passage between said zones, a cylinder associated with said structure, a communicating. port between said structure and said cylinder, a spring-pressed piston normally disposed in an intermediate position in-said cylinder, and means operative during circuit closing movement of said interrupter for driving said piston to said intermediate position within said cylinder so that during a circuit opening operation said piston may move immediately after separation of said contacts in one direction for augmenting the fluid pressure in said interrupter for lower current interruptions but may move a substantial distance in the opposite direction for moderating the fluid pressure in said interrupter for higher current interruptions.

4. A circuit interrupter comprising a pressure confining structur with an arc-extinguishing fluid contained therein, relatively movable contacts adapted to separate in said structure to produce a pressure-generating arc and'an interrupting arc, said structurev defining a pressure zone about said pressure-generating arc and an interrupting zone adjacent the interrupting arc, a communicating blast passage between said zones, a cylinder associated with said structure, a communicating port between said structure and said cylinder, a spring-pressed piston normally disposed in an intermediate position in said cylinder, means operative during circuit closing movement of said interrupter for driving said piston to said intermediate position within said cylinder so that during a circuit opening operation said piston may move in one direction immediately after separation of said contacts for augmenting the ffuid pressure in said interrupter for lower current interruptions, and venting means from the interior of said structure arranged to be opened in accordance with reverse movement of said piston for moderating the fiuid pressure in said interrupter for higher current interruptions.

5. A circuit interrupter comprising a pressure confining structure with an arc-extinguishing fluid contained therein, relatively movable contacts adapted to separate in said structure to produce a pressure-generating arc and an interrupting arc, said structure defining a pressure zone about said pressure generating arc and an interrupting zone adjacent the interrupting arc, a communicating blast passage between said zones, a cylinder associated with said structure, a first port opening connecting said cylinder with said interrupting zone, a second port opening connecting said cylinder with said pressure zone, a springpressed piston normally disposed in an intermediate position in said cylinder, and means operative during circuit closing movement of said inter= rupter for driving said piston to said intermediate position within said cylinder so that during a circuit opening operation said piston may move in one direction for augmenting the blast action through said first port simultaneously with the separation of said contacts when the current to be interrupted is below a predetermined value and in the opposite direction to open up said second port for moderating internal fluid pressures from said pressure zone when the current to be interrupted is above a predetermined value.

6. A circuit interrupter comprising a pressure confining structure, an arc extinguishing fluid contained by said structure, relatively movable contacts adapted to separate in said structure, means for separating said contacts to draw an arc to be extinguished by blast action within said structure, pressure applying means having a normal position and communicating with the interior of said structure, said normal position of said piston being the position thereof when the interrupter is closed, biasing means urging said pressure means in one direction from said normal position for applying a predetermined minimum pressure to said fluid during the first part of a current-interrupting operation, and venting means from the interior. of said structure arranged to be opened in accordance with movement of said pressure applying means in the opposite direction to a position beyond said normal position in response to pressurein said structure in excess of a predetermined value.

'7. A circuit interrupter comprising a pressure confining structure, an arc extinguishing fluid contained by said structure, relatively movable contacts adapted to separate in said structure, means for separating said contacts to draw an arc to be extinguishedby blast action within said structure, piston means having a normal position and communicating with the interior of;said structure, said normal position of said piston being the position thereof when the interrupter is closed, spring means biasing said piston in' one direction from said normal position for applying a predetermined minimum pressure tosaid fluid during the first part of a circuit interrupting operation, and venting means from the interior of said structure arranged to be opened in accordance with movement of said piston means in the opposite direction to a position beyond said normal position in response to pressure in said structure in excess of a predetermined Value.

8. A circuit interrupter comprising a pressureconfining structure, an arc-extinguishing fluid contained by said structure, relatively movable contacts adapted to separate in said structure, means for separating said contacts to drawan arc to be extinguished, means for regulating the volumetric capacity of said structure in accordanoe with the interrupting pressure generated therein, said last means comprising a wall portion of said structure having a normal position and movable therefrom in one direction simultaneously with separation of said contacts for appreciably, decreasing the volume-of said structure in response to pressure therein below a predetermined value and in another direction for appreciably increasing the volume of said structure in response to pressure therein above a predetermined value.

9. A circuit interrupter comprising a pressureconfining structure, an arc-extinguishing fluid contained by said structure, relatively movable contacts adapted to separate in said structure, means for separating said contacts to draw an arc to be extinguished by blast action Within said structure, pressure-applying means normally occupying a predetermined position and communicating-with the interior of said structure, biasing means urging said pressure means in one direction from its normal position for applying a predetermined minimum pressure to said fluid during the first part of a current interrupting operation in response to opening of said contacts, said pressure-applying means constituting a yieldable wall portion of said structure arranged so as to be movable in a reverse direction to positions beyond its normal position for affording pressure-relief in the event that the fluid pressure within said structure exceeds said predetermined minimum, and are control means for regulating the length and configuration of the arc in accordance with the value of the arc current.

10. A circuit interrupter comprising a pressureconfining structure, an arc-extinguishing fluid in said structure, and relatively movable contacts immersed in said fiuid and operable in said structure, meansfor separating said contacts to drawan arc to b extinguished by blastaction within said structure, movable. pressure-applying means. communicating. with the interior of said structure, biasing means urging said pressure means in one direction from. a normal position for applying a predetermined minimum pressure to said fluid during the first. part of a current interrupting operation, said. pressure-applying means constituting a'yie'ldable wall portion of said structure movable in. a reverse direction to positions beyond said normal position for affording pressure-relief in the event that the fluid pressure within said structure. exceeds said preseparate to form a pressure-generating arc. and

an interrupting arc in series, said contact structure being arranged with respect to the interrupter terminals so as to form a loop circuit through the interrupter, means for separating said contacts to produce a circuit interrupting operation by blast action within said structure, are control means for regulating the length and configuration of said pressure-generating are whereby the intensity of said blast action is influenced, said last-mentioned means comprising a generally cylindrical insulating guard member substantially encircling said arc, apertures through the wall of said guard member, and a main aperture in one portion of said guard being larger than the: apertures in the opposite portion thereof, the magnetic action of said loop circuit being effective to displace said pressure-generating arc toward said opposite portion of said guard.

12. Acircuit interrupter comprising av pressure confining structure, an arc-extinguishing fluid contained by saidstructure, relatively movable contact. structure disposed in said confining structure and adapted to separate to form a pressure. generating arc and an interrupting arc in series, said contact structure being arranged with respect tov the interrupter terminals so as to form a loop circuit. through the interrupter, means for separating said contacts to produce a circuit interrupting operation by blast action within said structure, and are control means for regulating the length and configuration of said pressure-generating arc whereby the intensity of said blast action is influenced, said last-mentioned means comprising a generally cylindrical insulating guard member substantially encircling said arc, said guard member having therein a narrow slot parallel to the pathv of; movement of said. contacts, the magnetic action of said loop circuit being effective to displace said pressuregenerating arc laterally in a direction toward said slot,

PERCY BARTLETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,271,989 Prince s Feb. 3, 1942 2,285,643 Beiersdorf et a1. June 9, 1942 2,412,858 Baker et al. Dec. 17, 1946 2,422,569 Leeds June 17, 1947 FOREIGN PATENTS.

Number Country Date 450,405 Great Britain July 16, 1936 500,731 Great Britain "Feb. 13, 1939 

